


I Wish You Would Write... 9

by equilateral_asshat



Series: I wish you would write... [9]
Category: Gravity Falls
Genre: At this point in time I would like to state I do not use the 'underage' tag, F/M, Lady Priscilla, because I never write the twins doing anything explicitly dirty WHILE 'underage', pinecest - Freeform, pinescest - Freeform
Language: English
Status: Completed
Published: 2018-12-16
Updated: 2018-12-16
Packaged: 2019-09-20 07:24:55
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 1,193
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/17018301
Author URL: https://archiveofourown.org/users/equilateral_asshat/pseuds/equilateral_asshat
Summary: The "I wish you would write" stories are small fics written from prompts sent by users who finish the statement with the type of fic they'd like to see.





	I Wish You Would Write... 9

**Author's Note:**

> Dipper try's to surprise Mabel and instead catches her doing something else.
> 
> [NSFW. Also, whoever referred to a certain part of Mabel as Lady Priscilla, I’m using that headcanon. If anybody knows who it was, lemme know and I’ll credit them!]

_She thinks she’s so clever, always jumping out from under my bed, or out from behind the shower curtain, I’ll give HER something to laugh about!_

Dipper wriggled into the space of his sister’s closet he’d hollowed out from the mountain of stuffed animals and sweaters it held, crouched silently in place. It was the perfect plan; he’d managed to sneak home ahead of his sister, and made sure to make it look like he hadn’t made it home yet either. With any luck, she’d be getting home any minute now.

The front door slammed shut, and he heard the telltale sound of her shoes being kicked against the wall in the mudroom, followed by her enthusiastically vaulting the stairs a few steps at a time. Thundering down the hallway, and then the sound of his own door being slammed open.

“AHA, thought you could get home early and… trick… me?” He bit down on his lips to avoid letting any laughter escape. The sounds of her shuffling about his room trying to draw him out of where ever she believed him to be hiding were like music to his ears. She didn’t suspect a thing.

“Okay, Dipper, if you’re here I give up, you win this time!” He stayed tight-lipped, determined to wait until the perfect moment to strike. “You really aren’t hiding anywhere?”

Thirty seconds or so of silence passed, and he heard her step into her own room and close the door, then swiftly latch the lock. He peered through the narrow space between the slats in the door to spy her peeling out of her socks.

“Then I guess it’s Mabel-time!” he heard her proudly proclaim. The perfect time to strike was nearly upon him, he just had to wait. A sense of pride built up in his stomach, but the next thing he saw quickly extinguished all of that.

Facing away from the closet door, Mabel was bent down, slipping her shorts down around her ankles, and then off. A winking pig face printed on the back of her panties was staring directly at him. There was a sinking feeling building in his insides; his little prank had gone from a joke to unwilling voyeurism!

Well… he hoped it was unwilling. Part of him refused to let him wrench his eyes away from the spectacle unfolding as her sweater joined the pile of clothing she had started on the floor. She was no supermodel, and she was no Wendy Corduroy, but damn if his twin didn’t have some good curves going!

  
… did his brain _REALLY_ just say that?! Oh god, this was getting worse by the second, because not only did he think it, his body reacted accordingly. He started thinking of anything he could to try and force the reaction down.

_Mermando’s gross mustache on my face, that spider lady that tried to eat Grunkle Stan, Manotaur sweat, Grunkle Stan naked…_

The entire time these thoughts cycled through his mind’s eye, his own two eyes were gliding over the various dips, swells and valleys of his sister’s form.

 _I’m fucking disgusting, why can’t I look away, good god…_ Every passing second saw her further disrobing; her bra was unlatched and dumped on the floor, and she gave a small twirl, which gave her brother a full view of everything she ever had hidden under her shirt. Before he was given anything else to look at, though, she flopped back on her bed with a sigh of relief, knees overhanging the edge facing the closet.

“Feels so good to let the girls breathe,” she murmured, giving her chest a quick squeeze. He tried, in vain, not to watch, but his eyes stayed firmly locked on what he could see. “Oh-ho, what’s that, lady Priscilla? You wanna come out too?” He’d never heard that name before, what was she talking about?

Hooking her thumbs into her waistband, she started to wiggle her panties down and OH. Oh, so _that_ was what she referred to by that name. He wanted nothing more than to avert his eyes, dig a hole in the closet wall and tunnel to freedom through the house’s foundation. This was wrong, he shouldn’t be watching this go on! He shouldn’t be so _into it._

Despite his brain knowing it was wrong, his body refused to comply. He leaned a little closer to the door, drinking in the details as she sat up, legs parted. What little bit of fuzz she had, she had trimmed into the shape of a shooting star, pointing downwards at her you-know-what. Everything else was clean shaven, to the point that you might swear the shape of her patch of hair was growing in that way naturally. As quickly as she had exposed herself unknowingly to him, her hand dipped down and hid it all from sight.

“My goodness, Priscilla! Such a sopping m-mess!” she exclaimed, a light giggle rising in her voice. He could hear _just_ how wet when her fingers slid over her muffin, and it sent a shiver down his spine. His pants were growing threateningly tight.

 _I guess just undoing them to make myself comfortable isn’t too bad of a thing_ , he convinced himself. His arousal sprung free, and he allowed himself to exhale through his nostrils, silently, with relief.

As he resumed watching the peepshow he had unknowingly created by hiding here, soon his hand was joining in the fun. He hated himself, but he just couldn’t stop. All the little moans and whimpers, plus the _gasps_ , it was too much to ignore.

“Nnggh, D-Dipper,” he heard her mutter, and he froze. Did she just say his name?! Did she know he was there?! “D-ipper, h-harder,” she followed, and he realized that he was still hidden. But she was rubbing herself to the thought of him doing this to her? How long had she been masturbating while thinking of him?! His hand tugged faster, breaths deepening.

A short gasp, followed by a high pitched shriek of pleasure cut through the air, snapping his thoughts back to the show. Her legs clamped together, and a low growl managed to gurgle out of her throat. “Oh gods, yes, fill me up, bro.”

Those words set something off in his brain, and his dick. Before he could stop himself, his climax rocked and his body went rigid, the first couple of shots plastering the inside of the closet door. He panicked, and tried to clamp his free hand over the end of his spasming member, but only succeeded in throwing himself off balance. He fell backwards with a _whumpf,_ one foot knocking into the door and causing it to rattle loudly. He muttered an “Aw, fuck,” under his breath.

In the next instant, the door flew open to reveal his sister, naked, one hand holding an oversized knitting needle-one for making large loop blankets and the like-in one hand as a bludgeon, the other braced on the door. The two siblings regarded one another, her eyes darting between his hands and his face, her own face red with embarrassment. Silence hung in the air.

Finally, Dipper spoke up.

“Um… boo?”


End file.
